Half of pregnant women have heartburn during pregnancy. Most primaparas and some multiparas are spontaneously relieved in the last weeks as the uterus descends, but all are invariably relieved immediately after delivery. The heartburn is a newly experienced burning sensation of variable severity in the throat or substernal region, frequently radiating from one area to the other.One-third of the women developed heartburn in the first 4 months of pregnancy; this appeared to be associated with psychic factors and was particularly resistant to antacid therapy. A neuromuscular mechanism is an attractive but unproved explanation. The character of heartburn in late pregnancy is different; clinical and objective evidence suggests that acid reflux is a mechanism, and antacids are effective. There is no evidence suggesting that neuromuscular dysfunction of the esophagus is involved.